This invention relates generally to the field of machinery for applying fibers to a shaft and more particularly to a machine for application of triaxially braided fibers to a shaft.
Both recreational and industrial activities employ tubular shaped shafts formed of fibers embedded in a matrix. Hockey sticks, lacrosse sticks, golf clubs, and ski poles can all be formed of tubular shafts formed of fibers embedded in matrix. Variations in the mechanical properties of the shaft can be achieved by varying the manner in which the fibers are woven together as a function of their location on the shaft, such as varying the fiber angle along the length of the shaft. Spoolable tubing utilized in industrial activities, such as oil well operations, can also be formed of fibers embedded in a matrix. Such spoolable tubing can be unspooled into an oil well and then spooled onto a reel for transportation to another oil well. Spoolable tubing extends down into the depths of the well for delivering liquids and for working over the interior surface of the well.
One method for manufacturing tubular shafts containing reinforcing fibers employs a technique wherein a mandrel is passed through a braider that applies fibers around the mandrel. For instance, Shobert, U.S. Pat. No. 3,007,497, discloses a reinforced plastic rod formed by passing a mandrel through a braiding machine which applies an axially oriented fiber along the longitudinal axis of the mandrel. The braiding machine also applies two helically oriented fibers around the mandrel. The angles traced by the two helically oriented fibers are determined by the interaction between the rotation of the braiding machine relative to the mandrel and the translational velocity of the mandrel as it passes through the braiding machine.
Other methods known in the art for manufacturing tubular shafts having reinforcing fibers employ a technique wherein a mandrel passes through various stations that apply fibers around the mandrel. For example, the mandrel is passed through a winding machine that applies an axial fiber and is then passed through a spinning braiding station that applies two helically oriented fibers. If desired, the axially oriented fiber applied by the winding machine can also be made to follow a helical path by rotating the mandrel relative to the winding machine as it passes through the winding machine. This process can be repeated to form additional layers, referred to in the industry as "plies", by passing the mandrel through additional pairs of winding machines and braiding stations.
It is apparent in the foregoing technique that the angle of the helix along which the axial, or primary, fibers are lain cannot readily be controlled independently of the angle of the helices along which the two helically oriented fibers are lain. This is because when the mandrel is rotated to adjust the spin rate of the braiding station, the winding rate of the winding station is changed, and vice versa.
As indicated above, in some applications, it is desirable to vary the mechanical properties of the shaft along its length by varying the angle of the primary fibers and the helically oriented fibers along the shaft's length. This requires the continuous adjustment of the braiding station's spin rate and the mandrel's rotation rate as the mandrel translates along its longitudinal axis. As a practical matter, continuous adjustment of this nature is difficult to achieve accurately enough for precise placement of the three fibers because of transients associated with any complex mechanical system.
A further disadvantage of some prior art techniques is manifested when more than one ply having cross-braided fibers is to be applied and where the primary fibers on each ply are to follow different helical paths. Since the mandrel is a rigid body, it is not possible to simultaneously rotate it at one rate to form the helical path in one ply and to rotate it at a different rate to form the helical path in another ply.
In some applications, it may be impractical to rotate the mandrel at all. For example, the mandrel could be too long to rotate easily or the mandrel may be extruded continuously through a die.
An object of the invention to provide an apparatus for applying a triaxial braid in which the pitch of the priority fiber can be controlled independently of the pitch of the helically oriented fibers.